U.S. patent application number 12/540743 was filed with the patent office on 2010-03-04 for dielectric ceramic, method for producing dielectric ceramic, and monolithic ceramic capacitor.
This patent application is currently assigned to MURATA MANUFACTURING CO., LTD.. Invention is credited to Masayuki Ishihara, Makoto Matsuda, Tomonori Muraki, Tomoyuki Nakamura, Takehisa Sasabayashi, Akihiro Shiota, Hironori Suzuki.
Application Number | 20100053843 12/540743 |
Document ID | / |
Family ID | 41725133 |
Filed Date | 2010-03-04 |
United States Patent
Application |
20100053843 |
Kind Code |
A1 |
Muraki; Tomonori ; et
al. |
March 4, 2010 |
DIELECTRIC CERAMIC, METHOD FOR PRODUCING DIELECTRIC CERAMIC, AND
MONOLITHIC CERAMIC CAPACITOR
Abstract
A dielectric ceramic contains a barium titanate and Li. In the
dielectric ceramic, the following inequalities are satisfied:
0.5.ltoreq.e.ltoreq.6.0, 0.06<Rg<0.17, and .sigma.g<0.075,
where e is the content, in molar parts, of Li with respect to 100
molar parts of the titanate; Rg is the average size, in .mu.m, of
grains in the dielectric ceramic; and .sigma.g is the standard
deviation, in .mu.m, of the size of the grains.
Inventors: |
Muraki; Tomonori; (Yasu-shi,
JP) ; Nakamura; Tomoyuki; (Moriyama-shi, JP) ;
Matsuda; Makoto; (Moriyama-shi, JP) ; Suzuki;
Hironori; (Yasu-shi, JP) ; Sasabayashi; Takehisa;
(Echizen-shi, JP) ; Ishihara; Masayuki; (Yasu-shi,
JP) ; Shiota; Akihiro; (Yasu-shi, JP) |
Correspondence
Address: |
DICKSTEIN SHAPIRO LLP
1633 Broadway
NEW YORK
NY
10019
US
|
Assignee: |
MURATA MANUFACTURING CO.,
LTD.
Nagaokakyo-Shi
JP
|
Family ID: |
41725133 |
Appl. No.: |
12/540743 |
Filed: |
August 13, 2009 |
Current U.S.
Class: |
361/321.4 ;
264/615; 501/137; 501/138; 501/139 |
Current CPC
Class: |
C04B 2235/781 20130101;
C04B 35/4682 20130101; C04B 2235/3262 20130101; C04B 2235/3227
20130101; B82Y 30/00 20130101; C04B 2235/3229 20130101; C04B
2235/3208 20130101; C04B 2235/3224 20130101; C04B 2235/79 20130101;
H01G 4/30 20130101; C04B 2235/5454 20130101; C04B 2235/3418
20130101; C04B 2235/5481 20130101; C04B 2235/6584 20130101; C04B
2235/6588 20130101; Y10T 29/435 20150115; C04B 2235/3239 20130101;
H01G 4/1227 20130101; C04B 2235/5445 20130101; C04B 2235/3206
20130101; C04B 2235/3203 20130101; C04B 2235/784 20130101; C04B
2235/785 20130101; C04B 2235/6582 20130101; C04B 2235/3225
20130101 |
Class at
Publication: |
361/321.4 ;
501/137; 501/138; 501/139; 264/615 |
International
Class: |
H01G 4/06 20060101
H01G004/06; C04B 35/468 20060101 C04B035/468 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 27, 2008 |
JP |
2008-217585 |
Claims
1. A dielectric ceramic containing: barium titanate; and Li,
wherein 0.5.ltoreq.e.ltoreq.6.2, 0.06<Rg<0.17, and
.sigma.g<0.075, where e is the content, in molar parts, of Li
with respect to 100 molar parts of the titanate; Rg is the average
size, in .mu.m, of grains in the dielectric ceramic; and .sigma.g
is the standard deviation, in .mu.m, of the size of the grains.
2. The dielectric ceramic according to claim 1, having the formula
100(Ba.sub.1-xCa.sub.x).sub.mTiO.sub.3+aRO.sub.3/2+bMgO+cMO+dSiO.sub.2+eL-
iO.sub.1/2, wherein m, a, b, c, d, and e are mole numbers; R is at
least one member selected from the group consisting of La, Ce, Pr,
Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y; M is at least
one of Mn and V; 0.96.ltoreq.m.ltoreq.1.03; 0.ltoreq.x.ltoreq.0.2;
0.2.ltoreq.a.ltoreq.5.0; 0.ltoreq.b.ltoreq.2.0;
0.2.ltoreq.c.ltoreq.1.0; and 0.5.ltoreq.d.ltoreq.4.0.
3. The dielectric ceramic according to claim 2, wherein
e.ltoreq.6.0, 0.06<Rg<0.14 and .sigma.g<0.075.
4. The dielectric ceramic according to claim 3, wherein M is a
combination of Mn and V; 1.00.ltoreq.m.ltoreq.1.03; and x is 0.
5. The dielectric ceramic according to claim 1, wherein
0.06.ltoreq.Rg.ltoreq.0.14 and .sigma.g<0.075.
6. The dielectric ceramic according to claim 5, wherein
e.ltoreq.6.0 and .sigma.g<0.06.
7. A monolithic ceramic capacitor comprising: a capacitor body
including a plurality of stacked dielectric ceramic layers and a
plurality of internal electrodes each of which extends between
adjacent dielectric ceramic layers; and a plurality of external
electrodes which are located on different surfaces of the capacitor
body and each of which is electrically connected to an internal
electrodes, wherein the dielectric ceramic layers located between
the internal electrodes adjacent to each other in the stacking
direction of the internal electrodes have a thickness of less than
1 .mu.m and are made of the dielectric ceramic according to claim
6.
8. A monolithic ceramic capacitor comprising: a capacitor body
including a plurality of stacked dielectric ceramic layers and a
plurality of internal electrodes each of which extends between
adjacent dielectric ceramic layers; and a plurality of external
electrodes which are located on different surfaces of the capacitor
body and each of which is electrically connected to an internal
electrodes, wherein the dielectric ceramic layers located between
the internal electrodes adjacent to each other in the stacking
direction of the internal electrodes have a thickness of less than
1 .mu.m and are made of the dielectric ceramic according to claim
5.
9. A monolithic ceramic capacitor comprising: a capacitor body
including a plurality of stacked dielectric ceramic layers and a
plurality of internal electrodes each of which extends between
adjacent dielectric ceramic layers; and a plurality of external
electrodes which are located on different surfaces of the capacitor
body and each of which is electrically connected to an internal
electrodes, wherein the dielectric ceramic layers located between
the internal electrodes adjacent to each other in the stacking
direction of the internal electrodes have a thickness of less than
1 .mu.m and are made of the dielectric ceramic according to claim
4.
10. A monolithic ceramic capacitor comprising: a capacitor body
including a plurality of stacked dielectric ceramic layers and a
plurality of internal electrodes each of which extends between
adjacent dielectric ceramic layers; and a plurality of external
electrodes which are located on different surfaces of the capacitor
body and each of which is electrically connected to an internal
electrodes, wherein the dielectric ceramic layers located between
the internal electrodes adjacent to each other in the stacking
direction of the internal electrodes have a thickness of less than
1 .mu.m and are made of the dielectric ceramic according to claim
3.
11. A monolithic ceramic capacitor comprising: a capacitor body
including a plurality of stacked dielectric ceramic layers and a
plurality of internal electrodes each of which extends between
adjacent dielectric ceramic layers; and a plurality of external
electrodes which are located on different surfaces of the capacitor
body and each of which is electrically connected to an internal
electrodes, wherein the dielectric ceramic layers located between
the internal electrodes adjacent to each other in the stacking
direction of the internal electrodes have a thickness of less than
1 .mu.m and are made of the dielectric ceramic according to claim
2.
12. A monolithic ceramic capacitor comprising: a capacitor body
including a plurality of stacked dielectric ceramic layers and a
plurality of internal electrodes each of which extends between
adjacent dielectric ceramic layers; and a plurality of external
electrodes which are located on different surfaces of the capacitor
body and each of which is electrically connected to an internal
electrodes, wherein the dielectric ceramic layers located between
the internal electrodes adjacent to each other in the stacking
direction of the internal electrodes have a thickness of less than
1 .mu.m and are made of the dielectric ceramic according to claim
1.
13. A method for producing a dielectric ceramic, comprising:
providing a ceramic source powder mixture of a ceramic powder
principally containing a barium titanate and a minor component
containing a Li compound; forming the ceramic source powder into a
ceramic form; and firing the ceramic form, wherein
0.5.ltoreq.e.ltoreq.6.2, 0.06<Rb<0.17, and .sigma.b<0.065,
where e is the content, in molar parts, of Li in the ceramic source
powder with respect to 100 molar parts of barium titanate; Rb is
the average particle size, in .mu.m, of the barium titanate ceramic
powder; and .sigma.b is the standard deviation, in .mu.m, of the
particle size of the barium titanate ceramic powder.
14. The method to claim 13, wherein e.ltoreq.6.0,
0.06<Rb<0.14 and .sigma.g<0.075.
15. The method to claim 14, wherein .sigma.g<0.075.
16. The method to claim 15, wherein the barium titanate is 100
moles of (Ba.sub.1-xCa.sub.x).sub.mTiO.sub.3 in which
0.96.ltoreq.m.ltoreq.1.03, and 0.ltoreq.x.ltoreq.0.2; the ceramic
source powder comprises aRO.sub.3/2, bMgO, cMO, and dSiO.sub.2,
wherein m, a, b, c, and d, are mole numbers; R is at least one
member selected from the group consisting of La, Ce, Pr, Nd, Sm,
Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y; M is at least one of Mn
and V; 0.2.ltoreq.a.ltoreq.5.0; 0.ltoreq.b.ltoreq.2.0;
0.2.ltoreq.c.ltoreq.1.0; and 0.5.ltoreq.d.ltoreq.4.0.
17. The method to claim 14, wherein the barium titanate is 100
moles of (Ba.sub.1-xCa.sub.x).sub.mTiO.sub.3 in which
0.96.ltoreq.m.ltoreq.1.03, and 0.ltoreq.x.ltoreq.0.2; the ceramic
source powder comprises comprises aRO.sub.3/2, bMgO, cMO, and
dSiO.sub.2, wherein m, a, b, c, and d, are mole numbers; R is at
least one member selected from the group consisting of La, Ce, Pr,
Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y; M is at least
one of Mn and V; 0.2.ltoreq.a.ltoreq.5.0; 0.ltoreq.b.ltoreq.2.0;
0.2.ltoreq.c.ltoreq.1.0; and 0.5.ltoreq.d.ltoreq.4.0.
18. The method to claim 13, wherein the barium titanate is 100
moles of (Ba.sub.1-xCa.sub.x).sub.mTiO.sub.3 in which
0.96.ltoreq.m.ltoreq.1.03, and 0.ltoreq.x.ltoreq.0.2; the ceramic
source powder comprises comprises aRO.sub.3/2, bMgO, cMO, and
dSiO.sub.2, wherein m, a, b, c, and d, are mole numbers; R is at
least one member selected from the group consisting of La, Ce, Pr,
Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y; M is at least
one of Mn and V; 0.2.ltoreq.a.ltoreq.5.0; 0.ltoreq.b.ltoreq.2.0;
0.2.ltoreq.c.ltoreq.1.0; and 0.5.ltoreq.d.ltoreq.4.0.
19. A method for producing a dielectric ceramic, comprising:
providing a ceramic powder principally containing a barium
titanate; providing a minor component containing a Li compound;
preparing a ceramic source powder by mixing the barium titanate
ceramic powder with the minor component; forming the ceramic source
powder into a ceramic form; and firing the ceramic form, wherein
0.5.ltoreq.e.ltoreq.6.2, 0.06<Rb<0.17, and .sigma.b<0.065,
where e is the content, in molar parts, of Li in the ceramic source
powder with respect to 100 molar parts of barium titanate; Rb is
the average particle size, in .mu.m, of the barium titanate ceramic
powder; and .sigma.b is the standard deviation, in .mu.m, of the
particle size of the barium titanate ceramic powder.
20. The method to claim 19, wherein the barium titanate is
(Ba.sub.1-xCa.sub.x).sub.mTiO.sub.3 in which
0.96.ltoreq.m.ltoreq.1.03, and 0.ltoreq.x.ltoreq.0.2; additionally
provided are aRO.sub.3/2, bMgO, cMO, and dSiO.sub.2, wherein a, b,
c, and d, are mole numbers; R is at least one member selected from
the group consisting of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er,
Tm, Yb, Lu, and Y; M is at least one of Mn and V;
0.2.ltoreq.a.ltoreq.5.0; 0.ltoreq.b.ltoreq.2.0;
0.2.ltoreq.c.ltoreq.1.0; and 0.5.ltoreq.d.ltoreq.4.0.; and the
additional provided aRO.sub.3/2, bMgO, cMO, and dSiO.sub.2 are
incorporated in the ceramic source powder before firing.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to dielectric ceramics,
methods for producing the dielectric ceramics, and monolithic
ceramic capacitors. The present invention particularly relates to
an improvement in thickness reduction for dielectric ceramic layers
for use in monolithic ceramic capacitors.
[0003] 2. Description of the Related Art
[0004] Monolithic ceramic capacitors include capacitor bodies
including a plurality of stacked dielectric ceramic layers and a
plurality of internal electrodes extending between the dielectric
ceramic layers. External electrodes are disposed on end surfaces of
the capacitor body that are opposed to each other. The external
electrode electrically connects the internal electrodes to each
other. Some of the internal electrodes are electrically connected
to one of the external electrodes and the other internal electrodes
are electrically connected to the other one. The internal
electrodes electrically connected to one of the external electrodes
and the internal electrodes electrically connected to the other one
are alternately arranged in the stacking direction of the
dielectric ceramic layers.
[0005] The conductive material contained in the internal electrodes
is usually Ni for cost reduction. In the manufacture of the
monolithic ceramic capacitors, the capacitor bodies are fired such
that the dielectric ceramic layers are sintered. The capacitor
bodies need to be fired at a time when the internal electrodes are
arranged in the capacitor bodies. Ni, which is contained in the
internal electrodes, is a base metal and therefore the capacitor
bodies need to be fired in reducing atmospheres.
[0006] The dielectric ceramic contained in the dielectric ceramic
layers is usually BaTiO.sub.3, which has a high dielectric
constant.
[0007] Thin dielectric ceramic layers are used to manufacture
monolithic ceramic capacitors with high capacitance per unit
volume.
[0008] It is effective to use the thin dielectric ceramic layers in
combination with thin internal electrodes. However, the thin
internal electrodes are likely to be spheroidized while being fired
in reducing atmospheres and therefore are readily broken. In order
to avoid such a problem, the thin dielectric ceramic layers can be
sintered by low-temperature firing. Adding sintering aids
containing, for example, SiO.sub.2, to ceramic materials is
effective to allow the ceramic materials to be sintered at low
temperature. Japanese Unexamined Patent Application Publication No.
2001-89231 (hereinafter referred to as Patent Document 1) discloses
that lithium is effective in achieving low-temperature
sintering.
[0009] In particular, Patent Document 1 discloses a dielectric
ceramic composition containing a lithium compound and a major
component containing 89% to 97% barium titanate in terms of
BaTiO.sub.3, 0.1% to 10% yttrium oxide in terms of Y.sub.2O.sub.3,
0.1% to 7% magnesium oxide in terms of MgO, 0.01% to 0.3% vanadium
oxide in terms of V.sub.2O.sub.5, 0.5% or less manganese oxide in
terms of MnO, and 0.5% to 7% barium calcium silicate in terms of
(Ba, Ca) SiO.sub.3, on a molar basis. The content of the lithium
compound is 0.01 to 5.0 weight percent in terms of Li.sub.2O with
respect to 100 mole percent of the major component.
[0010] Patent Document 1 indicates that lithium in the dielectric
ceramic composition acts as a sintering aid and is involved in
enhancing the temperature coefficient of dielectric constant of the
dielectric ceramic composition.
[0011] On the other hand, compact monolithic ceramic capacitors are
increasingly being demanded and therefore dielectric ceramic layers
with a thickness of less than about 1 .mu.m are demanded. The
electric field applied to a dielectric ceramic layer increases with
a reduction in the thickness of the dielectric ceramic layer.
Therefore, in order to cope with the above demand, dielectric
ceramics contained in the dielectric ceramic layers need to have
good insulating properties and life properties. However, there is a
problem in that the use of the dielectric ceramic composition
disclosed in Patent Document 1 is not effective in achieving
sufficient life properties.
SUMMARY OF THE INVENTION
[0012] Accordingly, it is an object of the present invention to
provide a dielectric ceramic capable of solving the above problem,
a method for producing the dielectric ceramic, and a monolithic
ceramic capacitor containing the dielectric ceramic.
[0013] An embodiment of the present invention is directed to a
dielectric ceramic containing BaTiO.sub.3 and Li. In the dielectric
ceramic, the following inequalities are satisfied:
0.5.ltoreq.e.ltoreq.6.2, 0.06<Rg<0.17, and .sigma.g<0.075,
where e is the content, in molar parts, of Li with respect to about
100 molar parts of BaTiO.sub.3; Rg is the average size, in .mu.m,
of grains in the dielectric ceramic; and .sigma.g is the standard
deviation, in .mu.m, of the size of the grains.
[0014] The dielectric ceramic preferably has the formula
100(Ba.sub.1-xCa.sub.x).sub.mTiO.sub.3+aRO.sub.3/2+bMgO+cMO+dSiO.sub.2+e-
LiO.sub.1/2,
wherein m, a, b, c, d, and e are mole numbers; R is at least one
selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Gd,
Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y; M is at least one of Mn and V;
0.96.ltoreq.m.ltoreq.1.03; 0.ltoreq.x.ltoreq.0.2;
0.2.ltoreq.a.ltoreq.5.0; 0.ltoreq.b.ltoreq.2.0;
0.2.ltoreq.c.ltoreq.1.0; and 0.5.ltoreq.d.ltoreq.4.0.
[0015] In the dielectric ceramic, the inequalities
0.06<Rg<0.14 and .sigma.g<0.075 are preferably
satisfied.
[0016] Another embodiment of the present invention is directed to a
monolithic ceramic capacitor. The monolithic ceramic capacitor
includes a capacitor body including a plurality of stacked
dielectric ceramic layers and a plurality of internal electrodes
extending between the dielectric ceramic layers and also includes a
plurality of external electrodes which are located on different
surfaces of the capacitor body and which are electrically connected
to the internal electrodes.
[0017] In the monolithic ceramic capacitor, the dielectric ceramic
layers located between the internal electrodes adjacent to each
other in the stacking direction of the internal electrodes have a
thickness of less than about 1 .mu.m and are made of the above
dielectric ceramic.
[0018] Another embodiment of the present invention is directed to a
method for producing a dielectric ceramic.
[0019] The method includes a step of preparing a ceramic powder
principally containing BaTiO.sub.3; a step of preparing a minor
component containing a Li compound; a step of preparing a ceramic
source powder by mixing the BaTiO.sub.3 ceramic powder with the
minor component; a step of forming the ceramic source powder into a
ceramic form; and a step of firing the ceramic form, wherein the
following inequalities are satisfied: 0.5.ltoreq.e.ltoreq.6.2,
0.06<Rb<0.17, and .sigma.b<0.065, where e is the content,
in molar parts, of Li in the ceramic source powder with respect to
100 molar parts of BaTiO.sub.3; Rb is the average particle size, in
.mu.m, of the BaTiO.sub.3 ceramic powder; and .sigma.b is the
standard deviation, in .mu.m, of the particle size of the
BaTiO.sub.3 ceramic powder.
[0020] A dielectric ceramic according to an embodiment of the
present invention contains Li and has a sufficiently small grain
size and substantially no coarse grains are present in the
dielectric ceramic. Therefore, in the case where the dielectric
ceramic is used to form dielectric ceramic layers for use in a
monolithic ceramic capacitor, the monolithic ceramic capacitor can
achieve good life properties even if the dielectric ceramic layers
have a thickness of less than about 1 .mu.m.
[0021] The dielectric ceramic has the formula
100(Ba.sub.1-xCa.sub.x).sub.mTiO.sub.3+aRO.sub.3/2+bMgO+cMO+dSiO.sub.2+eL-
iO.sub.1/2, wherein m, a, b, c, d, and e are mole numbers; R is at
least one selected from the group consisting of La, Ce, Pr, Nd, Sm,
Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y; M is at least one of Mn
and V; 0.96.ltoreq.m.ltoreq.1.03; 0.ltoreq.x.ltoreq.0.2;
0.2.ltoreq.a.ltoreq.5.0; 0.ltoreq.b.ltoreq.2.0;
0.2.ltoreq.c.ltoreq.1.0; and 0.5.ltoreq.d.ltoreq.4.0. This allows
the monolithic ceramic capacitor to achieve better life
properties.
[0022] In the dielectric ceramic, the inequalities
0.06<Rg<0.17 and .sigma.g<0.075 are preferably satisfied.
This allows the monolithic ceramic capacitor to achieve better life
properties.
[0023] In a method for producing a dielectric ceramic according to
an embodiment of the present invention, an appropriate amount of Li
is added to a major component powder with a sharp particle size
distribution; hence, grains with a sharp size distribution can be
obtained because particles are appropriately prevented from growing
during firing. Therefore, in the case where a dielectric ceramic
produced by the method is used to form dielectric ceramic layers
for use in a monolithic ceramic capacitor, the monolithic ceramic
capacitor can achieve good life properties even if the dielectric
ceramic layers have a thickness of less than about 1 .mu.m.
[0024] Other features, elements, characteristics and advantages of
the present invention will become more apparent from the following
detailed description of preferred embodiments of the present
invention with reference to the attached drawing.
BRIEF DESCRIPTION OF THE DRAWING
[0025] FIG. 1 is a schematic sectional view of a monolithic ceramic
capacitor according to an embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0026] FIG. 1 shows a monolithic ceramic capacitor 1 according to
an embodiment of the present invention in cross section.
[0027] The monolithic ceramic capacitor 1 includes a capacitor body
5 including a plurality of stacked dielectric ceramic layers 2, a
plurality of first internal electrodes 3, and a plurality of second
internal electrodes 4. The first and second internal electrodes 3
and 4 extend between the dielectric ceramic layers 2 and are made
of, for example, Ni.
[0028] The monolithic ceramic capacitor 1 further includes a first
external electrode 6 and second external electrode 7 located on
different surfaces of the capacitor body 5. The first and second
external electrodes 6 and 7 are made of, for example, Cu. In the
monolithic ceramic capacitor 1, the first and second external
electrodes 6 and 7 are disposed on end surfaces of the capacitor
body 5 that are opposed to each other as shown in FIG. 1. The first
internal electrodes 3 are electrically connected to the first
external electrode 6 and the second internal electrodes 4 are
electrically connected to the second external electrode 7. The
first and second internal electrodes 3 and 4 are alternately
arranged in the stacking direction of the dielectric ceramic layers
2.
[0029] In the monolithic ceramic capacitor 1, the dielectric
ceramic layers 2 located between the first and second internal
electrodes 3 and 4 adjacent to each other have a thickness of less
than about 1 .mu.m.
[0030] The dielectric ceramic layers 2 are made of a dielectric
ceramic containing BaTiO.sub.3, which is a major component, and Li,
which is derived from a minor component. In the dielectric ceramic,
the following inequalities are satisfied: 0.5.ltoreq.e.ltoreq.6.2,
0.06<Rg<0.17, and .sigma.g<0.075, wherein e is the
content, in molar parts, of Li with respect to about 100 molar
parts of BaTiO.sub.3; Rg is the average size, in .mu.m, of grains
in the dielectric ceramic; and .sigma.g is the standard deviation,
in .mu.m, of the size of the grains.
[0031] Since the dielectric ceramic, which is contained in the
dielectric ceramic layers 2, contains Li and has a sufficiently
small grain size and no coarse grains are present in the dielectric
ceramic, the monolithic ceramic capacitor 1 has good life
properties although the dielectric ceramic layers 2 have a small
thickness of less than about 1 .mu.m.
[0032] In view of the enhancement of life properties, the
dielectric ceramic preferably has the formula
100(Ba.sub.1-xCa.sub.x).sub.mTiO.sub.3+aRO.sub.3/2+bMgO+cMO+dSiO.sub.2+eL-
iO.sub.1/2, wherein m, a, b, c, d, and e are mole numbers; R is at
least one selected from the group consisting of La, Ce, Pr, Nd, Sm,
Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y; M is at least one of Mn
and V; 0.96.ltoreq.m.ltoreq.1.03; 0.ltoreq.x.ltoreq.0.2;
0.2.ltoreq.a.ltoreq.5.0; 0.ltoreq.b.ltoreq.2.0;
0.2.ltoreq.c.ltoreq.1.0; and 0.5.ltoreq.d.ltoreq.4.0.
[0033] In view of the enhancement of life properties, the
inequalities 0.06<Rg<0.14 and .sigma.g<0.75 are preferably
satisfied, Rg and .sigma.b being as described above.
[0034] In the manufacture of the monolithic ceramic capacitor 1,
the green capacitor body 5 is prepared and then fired. The green
capacitor body 5 is obtained in such a manner that green ceramic
sheets including green ceramic sheets having conductive paste films
for forming the first or second internal electrodes 3 or 4 are
stacked. The green ceramic sheets are converted into the dielectric
ceramic layers 2, which are included in the capacitor body 5, by
firing.
[0035] In order to prepare the green ceramic sheets, a BaTiO.sub.3
ceramic powder made of BaTiO.sub.3 is prepared. In the BaTiO.sub.3
ceramic powder, the following inequalities are satisfied:
0.06<Rb<0.17 and .sigma.b<0.065, wherein Rb is the average
particle size, in .mu.m, of the BaTiO.sub.3 ceramic powder and
.sigma.b is the standard deviation, in .mu.m, of the particle size
of the BaTiO.sub.3 ceramic powder.
[0036] The minor component is prepared. The minor component
contains a Li compound.
[0037] The BaTiO.sub.3 ceramic powder is mixed with the minor
component, whereby a ceramic source powder is obtained. In the
ceramic source powder, the inequality 0.5.ltoreq.e.ltoreq.6.2 is
satisfied, wherein e is the content, in molar parts, of Li in the
ceramic source powder with respect to about 100 molar parts of
BaTiO.sub.3.
[0038] The ceramic source powder is mixed with a binder and an
organic solvent, whereby a ceramic slurry is prepared. The ceramic
slurry is sheeted, whereby the green ceramic sheets are
obtained.
[0039] Since the green ceramic sheets contain the BaTiO.sub.3
ceramic powder and an appropriate amount of Li and the BaTiO.sub.3
ceramic powder has a sharp particle size distribution, particles of
the BaTiO.sub.3 ceramic powder are appropriately prevented from
growing during the firing step in which the capacitor body 5 is
prepared; hence, grains (particles in a sintered body) having a
sharp size distribution are obtained. Therefore, although the
dielectric ceramic layers 2 have a small thickness of less than
about 1 .mu.m, the monolithic ceramic capacitor 1 can achieve good
life properties.
[0040] The monolithic ceramic capacitor 1 is not limited to that
having a structure shown in FIG. 1. The monolithic ceramic
capacitor 1 may be a capacitor having a structure in which a
plurality of internal electrodes arranged in a capacitor body form
a series capacitance, an array-type monolithic ceramic capacitor,
or a monolithic ceramic capacitor having low equivalent series
inductance (ESL) and a multi-terminal structure.
EXPERIMENTS
[0041] Experiments based on the present invention are described
below.
Experiment 1
[0042] Experiment 1 was performed to investigate the influences of
the size distribution of grains and the content of Li on life
properties.
(A) Preparation of Dielectric Source Compositions
[0043] Ba.sub.1.007TiO.sub.3 powders having average particle sizes
Rg and standard deviations .sigma.b shown in Table 1 were prepared
from BaCO.sub.3 and TiO.sub.2, which were starting materials for a
major component. The average particle size Rg of each
Ba.sub.1.007TiO.sub.3 powder and the standard deviation .sigma.b of
the particle size of the Ba.sub.1.007TiO.sub.3 powder were
determined in such a manner that about 300 particles of the
Ba1.007TiO.sub.3 powder were analyzed with a field
emission-scanning electron microscope (FE-SEM) and the average
equivalent circle diameter of the particles was calculated. After
being weighed, the Ba.sub.1.007TiO.sub.3 powder was wet-mixed with
water in a ball mill, whereby aggregates of the
Ba.sub.1.007TiO.sub.3 powder were broken.
[0044] Powders of Dy.sub.2O.sub.3, MgCO.sub.3, MnCO.sub.3,
SiO.sub.2, and Li.sub.2CO.sub.3, which were starting materials for
minor components, were prepared. These powders were mixed with the
Ba.sub.1.007TiO.sub.3 powder such that the mixture had the formula
100Ba.sub.1.007TiO.sub.3+1.0DyO.sub.3/2+0.7MgO+0.3MnO+1.5SiO.sub.2+eLiO.s-
ub.1/2 and a Li content, represented by e in this formula, shown in
Table 1. The mixture was mixed with water in a ball mill and then
dried. Dielectric source compositions for Samples 1 to 18 were
prepared as described above. Samples 1 to 18 were substantially the
same in average particle size Rg, standard deviation .sigma.b, and
Li content e. Samples 1 to 9 are different in ceramic layer
thickness from Samples 10 to 18.
TABLE-US-00001 TABLE 1 Average particle Standard Ceramic layer size
Rg deviation .sigma.b Li content e thickness Samples (.mu.m)
(.mu.m) (molar parts) (.mu.m) 1 0.1 0.04 3.5 0.9 2 0.1 0.065 3.5
0.9 3 0.06 0.03 3.5 0.9 4 0.17 0.04 3.5 0.9 5 0.17 0.07 3.5 0.9 6
0.1 0.04 0.4 0.9 7 0.1 0.04 6.2 0.9 8 0.1 0.05 0.4 0.9 9 0.17 0.075
0.4 0.9 10 0.1 0.04 3.5 1.0 11 0.1 0.065 3.5 1.0 12 0.06 0.03 3.5
1.0 13 0.17 0.04 3.5 1.0 14 0.17 0.07 3.5 1.0 15 0.1 0.04 0.4 1.0
16 0.1 0.04 6.2 1.0 17 0.1 0.05 0.4 1.0 18 0.17 0.075 0.4 1.0
(B) Preparation of Samples
[0045] Each dielectric source composition was wet-mixed with a
polyvinyl butyral binder and ethanol in a ball mill, whereby a
ceramic slurry was prepared. The ceramic slurry was sheeted with a
lip coater, whereby two types of green ceramic sheets were prepared
such that fired ceramic sheets had a thickness of about 0.9 or 1.0
.mu.m.
[0046] A conductive paste principally containing Ni was applied to
the green ceramic sheets by screen printing, whereby conductive
paste films for forming internal electrodes were formed.
[0047] The green ceramic sheets having the conductive paste films
were stacked such that exposed ends of the conductive paste films
are alternately arranged, whereby green capacitor bodies were
prepared. The green capacitor bodies were heated at about
300.degree. C. in an N.sub.2 atmosphere, whereby the polyvinyl
butyral binder was burned out. The resulting green capacitor bodies
were fired at about 1,025.degree. C. for about two hours in a
reducing atmosphere, containing H.sub.2, N.sub.2, and H.sub.2O,
with an oxygen partial pressure of about 10.sup.-10 MPa, whereby
sintered capacitor bodies were obtained.
[0048] A Cu paste containing a
B.sub.2O.sub.3--Li.sub.2O--SiO.sub.2--BaO glass frit was applied to
both end surfaces of each of the sintered capacitor bodies, which
were then baked at about 800.degree. C. in an N.sub.2 atmosphere
such that external electrodes were formed so as to be electrically
connected to the internal electrodes, whereby Samples 1 to 18 were
obtained. Samples 1 to 18 were monolithic ceramic capacitors.
[0049] Samples 1 to 18 had a length of about 2.0 mm, a width of
about 1.2 mm, and a thickness of about 1.0 mm and included
dielectric ceramic layers, disposed between the internal
electrodes, having a thickness shown in Table 2. The number of the
effective dielectric ceramic layers of each sample was about 100.
The dielectric ceramic layers each had an electrode area of about
1.4 mm.sup.2.
(C) Evaluation of Samples
[0050] Samples 1 to 18 were evaluated for dielectric constant,
dielectric loss DF, temperature coefficient of capacitance, mean
time to failure, and microstructure.
[0051] In order to determine the dielectric constant of each
sample, the sample was measured for capacitance and dielectric loss
DF under the following conditions: a temperature of about
25.degree. C., a frequency of about 1 kHz, and an AC voltage of
about 0.5 Vrms.
[0052] The temperature coefficient of capacitance of the sample is
the change in capacitance associated with a temperature change. In
particular, the temperature coefficient of capacitance thereof was
determined to be the maximum change in capacitance over a range
from about -55.degree. C. to about 85.degree. C. relative to the
capacitance at about 25.degree. C. A capacitance change of about
-15% to 15% over a range from about -55.degree. C. to about
85.degree. C. meets the X5R characteristic of EIA standards.
[0053] In order to evaluate Samples 1 to 18 for high-temperature
load life, Samples 1 to 18 were subjected to an accelerated
reliability test in such a manner that the change in insulation
resistance of each sample was monitored with time while a
direct-current voltage of about 12.5 V was applied to the sample at
about 150.degree. C. In the accelerated reliability test, a sample
with an insulation resistance of about 10.sup.5 .OMEGA. or less was
determined to be defective and the mean time taken for the sample
to fail, that is, the mean time to failure of the sample was
determined.
[0054] Samples 1 to 18 were analyzed for ceramic microstructure.
The average grain size Rg of each sample and the standard deviation
.sigma.g of the grain size of the sample were determined in such a
manner that a surface of the sample was observed with an FE-SEM and
the average equivalent circle diameter of about 300 gains in the
sample was calculated.
[0055] The evaluation results are summarized in Table 2.
TABLE-US-00002 TABLE 2 Average Standard Di- Temperature Mean grain
deviation Di- electric coefficient of time to size Rg .sigma.g
electric loss DF capacitance failure Samples (.mu.m) (.mu.m)
constant (%) (%) (hours) 1 0.1 0.04 1800 1.8 -8 170 2 0.1 0.075
1900 1.9 -10 50 3 0.06 0.035 2300 2.2 -14 10 4 0.17 0.045 1900 2
-11 60 5 0.17 0.08 2000 2 -12 10 6 0.1 0.045 2000 2 -12 30 7 0.1
0.05 1800 1.9 -11 70 8 0.1 0.06 2100 2.1 -13 20 9 0.17 0.08 2400
2.3 -14 10 10 0.1 0.045 1800 1.8 -8 200 11 0.1 0.075 1900 1.9 -10
160 12 0.06 0.04 2300 2.2 -14 50 13 0.17 0.05 1900 2 -11 160 14
0.17 0.075 2000 2 -12 150 15 0.1 0.04 2000 2 -12 160 16 0.1 0.05
1800 1.9 -11 160 17 0.1 0.06 2100 2.1 -13 70 18 0.17 0.08 2400 2.3
-14 70
[0056] All the samples shown in Table 2 have a dielectric constant
of about 1,500 or more, a dielectric loss of less than about 5%,
and a temperature coefficient of capacitance meeting the X5R
characteristic.
[0057] Samples 1 to 9 have a ceramic layer thickness of about 0.9
.mu.m. In particular, Sample 1 satisfies the following three
conditions and has good life properties: 0.5.ltoreq.e.ltoreq.6.2,
0.06<Rg<0.17, and .sigma.g<0.075, wherein e is the Li
content in molar parts, Rb is the average grain size in .mu.m, and
.sigma.g is the standard deviation in .mu.m. This shows that the
synergy of the three factors Rg, .sigma.g, and e allows thin
capacitors with a ceramic layer thickness of less than about 1
.mu.m to have good life properties.
[0058] The reason for the above is probably as described below.
When Li is present in a minor component and the content of Li
therein is within a range defined by the inequality
0.5.ltoreq.e.ltoreq.6.2, Li acts as an inhibitor to prevent the
growth of grains and therefore the size distribution of the grains
is narrow. A reduction in grain size distribution leads to an
enhancement in reliability. In the case where a ceramic source
powder principally containing a barium titanate ceramic is used
when Li is present in the minor component within the range defined
by the inequality 0.5.ltoreq.e.ltoreq.6.1, the size distribution of
grains in a sintered dielectric ceramic is remarkably narrow and
therefore even a ceramic layer with a thickness of less than about
1.0 .mu.m has a mean time to failure of about 100 hours or more as
determined by the accelerated reliability test, that is, such a
ceramic layer can be improved in reliability. In the ceramic source
powder, the inequalities 0.06<Rg<0.17, and .sigma.g<0.075
are satisfied, wherein Rg is the average grain size in .mu.m and
.sigma.g is the standard deviation in .mu.m.
[0059] Samples 10 to 18 have a ceramic layer thickness of about 1.0
.mu.m. In particular, Sample 10, as well as Sample 1, satisfies the
following three conditions and has good life properties:
0.5.ltoreq.e.ltoreq.6.2, 0.06<Rg<0.17, and .sigma.g<0.075,
wherein e is the Li content in molar parts, Rg is the average grain
size in .mu.m, and .sigma.g is the standard deviation in .mu.m. For
life properties, the difference between Sample 1, which has a
ceramic layer thickness of less than about 1.0 .mu.m and satisfies
the three conditions, and Samples 2 to 9, which have a ceramic
layer thickness of less than about 1.0 .mu.m and satisfy none of
the three conditions, is more significant than the difference
between Sample 10, which has a ceramic layer thickness of about 1.0
.mu.m or more and satisfies the three conditions, and Samples 11 to
18, which have a ceramic layer thickness of about 1.0 .mu.m or more
and satisfy none of the three conditions.
Experiment 2
[0060] Experiment 2 was performed to specify a composition range
which is preferable in enhancing life properties.
(A) Preparation of Dielectric Source Compositions
[0061] Powders of BaCO.sub.3, CaCO.sub.3, and TiO.sub.2, which were
starting materials for a major component, were prepared and then
weighed such that (Ba.sub.1-xCa.sub.x).sub.mTiO.sub.3 compositions
were obtained, m and x being as shown in Table 3. The weighed
BaCO.sub.3, CaCO.sub.3, and TiO.sub.2 powders were heat-treated,
whereby (Ba.sub.1-xCa.sub.x).sub.mTiO.sub.3 powders having average
particle sizes Rb and standard deviations .sigma.b shown in Table 3
were obtained. After being weighed, each
(Ba.sub.1-xCa.sub.x).sub.mTiO.sub.3 powder was wet-mixed with water
in a ball mill, whereby aggregates of the
(Ba.sub.1-xCa.sub.x).sub.mTiO.sub.3 powder were broken.
[0062] Powders of the following compounds were prepared: an oxide
or carbonate of R, an oxide or carbonate of Mg, an oxide or
carbonate of M, an oxide or carbonate of Si, and an oxide or
carbonate of Li, R being at least one selected from the group
consisting of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb,
Lu, and Y, M being at least one of Mn and V, these compounds being
starting materials for minor components. These powders were mixed
with the (Ba.sub.1-xCa.sub.x).sub.mTiO.sub.3 powder such that the
mixture had the formula
100(Ba.sub.1-xCa.sub.x).sub.mTiO.sub.3+aRO.sub.3/2+bMgO+cMO+dSiO.sub.2+eL-
iO.sub.1/2 and contained an M component and R component shown in
Table 3, a, b, c, d, and e being as shown in Table 3. The mixture
was mixed with water in a ball mill and then dried. Dielectric
source compositions for Samples 101 to 128 were prepared as
described above.
TABLE-US-00003 TABLE 3 Average particle Standard Breakdown of
Breakdown of size Rg deviation .sigma.b component component Samples
(.mu.m) (.mu.m) m x a b c d e represented by M represented by R 101
0.11 0.04 0.960 0.00 1.0 0.8 0.4 1.5 3.5 0.2Mn, 0.2V 1.0La 102 0.11
0.04 1.030 0.00 1.0 0.8 0.4 1.5 3.5 0.2Mn, 0.2V 1.0Ce 103 0.11 0.04
1.007 0.00 1.0 0.8 0.4 1.5 3.5 0.2Mn, 0.2V 1.0Pr 104 0.10 0.04
1.007 0.20 1.0 0.8 0.4 1.5 3.5 0.2Mn, 0.2V 1.0Nd 105 0.10 0.04
1.007 0.10 0.2 0.8 0.4 1.5 3.5 0.2Mn, 0.2V 0.2Sm 106 0.11 0.04
1.007 0.00 5.0 0.8 0.4 1.5 3.5 0.2Mn, 0.2V 5.0Eu 107 0.11 0.04
1.007 0.00 1.0 0.0 0.4 1.5 3.5 0.2Mn, 0.2V 1.0Gd 108 0.11 0.04
1.007 0.00 1.0 2.0 0.4 1.5 3.5 0.2Mn, 0.2V 1.0Tb 109 0.11 0.04
1.007 0.00 1.0 0.8 0.2 1.5 3.5 0.1Mn, 0.1V 1.0Dy 110 0.11 0.04
1.007 0.00 1.0 0.8 1.0 1.5 3.5 0.4Mn, 0.4V 1.0Ho 111 0.11 0.04
1.007 0.00 1.0 0.8 0.4 1.5 3.5 0.4V 1.0Er 112 0.11 0.04 1.007 0.00
1.0 0.8 0.4 1.5 3.5 0.4Mn 1.0Tm 113 0.11 0.04 1.007 0.00 2.0 0.8
0.4 0.5 3.5 0.2Mn, 0.2V 2.0Yb 114 0.11 0.04 1.007 0.00 2.0 0.8 0.4
4.0 3.5 0.2Mn, 0.2V 2.0Lu 115 0.11 0.04 1.007 0.00 2.0 0.8 0.4 2.0
0.5 0.2Mn, 0.2V 2.0Y 116 0.11 0.04 1.007 0.00 2.0 0.8 0.4 2.0 6.0
0.2Mn, 0.2V 1.0Y, 1.0Dy 117 0.11 0.04 1.007 0.00 2.0 0.8 0.4 2.0
6.0 0.2Mn, 0.2V 1.0Sm, 1.0Gd 118 0.11 0.04 1.007 0.00 2.0 0.8 0.4
2.0 6.0 0.2Mn, 0.2V 1.0Y, 1.0Gd 119 0.10 0.04 0.959 0.10 1.0 0.8
0.4 1.5 3.5 0.2Mn, 0.2V 1.0Tb 120 0.10 0.04 1.031 0.10 1.0 0.8 0.4
1.5 3.5 0.2Mn, 0.2V 1.0Dy 121 0.10 0.04 1.007 0.21 1.0 0.8 0.4 1.5
3.5 0.2Mn, 0.2V 1.0Ho 122 0.11 0.04 1.007 0.00 0.1 0.8 0.4 1.5 3.5
0.2Mn, 0.2V 0.1Ho 123 0.11 0.04 1.007 0.00 5.1 0.8 0.4 1.5 3.5
0.2Mn, 0.2V 5.1Ho 124 0.11 0.04 1.007 0.00 1.0 2.1 0.4 1.5 3.5
0.2Mn, 0.2V 1.0Yb 125 0.11 0.04 1.007 0.00 1.0 0.8 0.1 1.5 3.5
0.05Mn, 0.05V 1.0Tb 126 0.11 0.04 1.007 0.00 1.0 0.8 1.1 1.5 3.5
0.5Mn, 0.6V 1.0Dy 127 0.11 0.04 1.007 0.00 1.0 0.8 0.4 0.4 3.5
0.2Mn, 0.2V 1.0Ho 128 0.11 0.04 1.007 0.00 1.0 0.8 0.4 4.1 3.5
0.2Mn, 0.2V 1.0Er
(B) Preparation of Samples
[0063] Samples 101 to 128 were prepared in substantially the same
manner as that described in Experiment 1. Samples 101 to 128 were
monolithic ceramic capacitors including dielectric ceramic layers
with a thickness of about 0.8 .mu.m.
(C) Evaluation of Samples
[0064] Samples 101 to 128 were evaluated in substantially the same
manner as that described in Experiment 1. The evaluation results
are summarized in Table 4.
TABLE-US-00004 TABLE 4 Average Standard Di- Temperature Mean grain
deviation Di- electric coefficient of time to size Rg .sigma.g
electric loss DF capacitance failure Samples (.mu.m) (.mu.m)
constant (%) (%) (hours) 101 0.11 0.04 2200 2.3 -9 160 102 0.11
0.04 1700 1.8 -8 190 103 0.11 0.04 1900 2.0 -9 180 104 0.10 0.04
2000 2.3 -9 170 105 0.10 0.04 1900 2.1 -10 180 106 0.11 0.04 1900
1.8 -13 160 107 0.11 0.04 2000 1.8 -9 160 108 0.11 0.04 1800 1.7
-10 180 109 0.11 0.04 2100 2.1 -10 160 110 0.11 0.04 1800 1.8 -8
180 111 0.11 0.04 1900 2.0 -8 190 112 0.11 0.04 1900 2.0 -9 180 113
0.11 0.04 2000 2.2 -11 160 114 0.11 0.04 2200 2.3 -13 160 115 0.11
0.04 2100 2.1 -11 160 116 0.11 0.04 1800 1.9 -12 190 117 0.11 0.04
1700 1.9 -13 180 118 0.11 0.04 1800 1.9 -12 180 119 0.10 0.04 1900
2.0 -14 130 120 0.10 0.04 1400 1.5 -10 120 121 0.10 0.04 1600 1.7
-14 130 122 0.11 0.04 1900 1.9 -12 110 123 0.11 0.04 1700 1.8 -17
140 124 0.11 0.04 1600 1.7 -14 120 125 0.11 0.04 1800 1.8 -13 110
126 0.11 0.04 1900 1.9 -13 120 127 0.11 0.04 1700 1.8 -14 110 128
0.11 0.04 2000 2.0 -16 110
[0065] All the samples shown in Table 4 are within the scope of the
present invention and have a dielectric loss of less than about 5%
and a mean time to failure of about 110 hours or more.
[0066] Samples 101 to 118 have the
100(Ba.sub.1-xCa.sub.x).sub.mTiO.sub.3+aRO.sub.3/2+bMgO+cMO+dSiO.sub.2+eL-
iO.sub.1/2, wherein 0.96.ltoreq.m.ltoreq.1.03,
0.ltoreq.x.ltoreq.0.2, 0.2.ltoreq.a.ltoreq.5.0,
0.ltoreq.b.ltoreq.2.0, 0.2.ltoreq.c.ltoreq.1.0, and
0.5.ltoreq.d.ltoreq.4.0. Therefore, Samples 101 to 118 have a
dielectric constant of about 1,500 or more, a temperature
coefficient of capacitance meeting the X5R characteristic, and a
mean time to failure of about 150 hours or more, that is, improved
life properties.
[0067] Sample 119, in which m<0.960, has a mean time to failure
of less than about 150 hours. Sample 120, in which m>1.030, has
a dielectric constant of less than about 1,500 and a mean time to
failure of less than about 150 hours.
[0068] Sample 121, in which x>0.20, has a mean time to failure
of less than about 150 hours.
[0069] Sample 122, in which a<0.2, has a mean time to failure of
less than about 150 hours. Sample 123, in which a>5.0, has a
temperature coefficient of dielectric constant with an absolute
value of about 15% or more and a mean time to failure of less than
about 150 hours.
[0070] Sample 124, in which b>2.0, has a mean time to failure of
less than about 150 hours.
[0071] Sample 125, in which c<0.2, has a mean time to failure of
less than about 150 hours. Sample 126, in which c>1.0, has a
mean time to failure of less than about 150 hours.
[0072] Sample 127, in which d<0.5, has a mean time to failure of
less than about 150 hours. Sample 128, in which d>4.0, has a
temperature coefficient of dielectric constant with an absolute
value of about 15% or more and a mean time to failure of less than
about 150 hours.
Experiment 3
[0073] Experiment 3 was performed to determine the preferable range
of the average size of grains.
(A) Preparation of Dielectric Source Compositions
[0074] Dielectric source compositions for Samples 201 and 202 were
prepared in substantially the same manner as that used to prepare
Sample 1 in Experiment 1 except that BaTiO.sub.3 powders having
average particle sizes Rg and standard deviations .sigma.b shown in
Table 5 were used.
TABLE-US-00005 TABLE 5 Average particle size Rg Standard deviation
.sigma.b Samples (.mu.m) (.mu.m) 201 0.07 0.03 202 0.15 0.06
(B) Preparation of Samples
[0075] Samples 201 to 202 were prepared in substantially the same
manner as that described in Experiment 1. Samples 201 to 202 were
monolithic ceramic capacitors including dielectric ceramic layers
with a thickness of about 0.9 .mu.m.
(C) Evaluation of Samples
[0076] Samples 201 to 202 were evaluated in substantially the same
manner as that described in Experiment 1. The evaluation results
are summarized in Table 6.
TABLE-US-00006 TABLE 6 Standard Di- Temperature Mean Average
deviation Di- electric coefficient of time to grain .sigma.g
electric loss DF capacitance failure Samples size Rg (.mu.m)
constant (%) (%) (hours) 201 0.07 0.03 1700 1.8 -7 170 202 0.15
0.06 2200 2.3 -11 120
[0077] As shown in Table 6, Sample 201 satisfies the inequality
0.06<Rg<0.15, wherein Rg is the average grain size in .mu.m.
Sample 202 does not satisfy this inequality. Sample 201 has better
life properties as compared to Sample 202.
[0078] While preferred embodiments of the invention have been
described above, it is to be understood that variations and
modifications will be apparent to those skilled in the art without
departing from the scope and spirit of the invention. The scope of
the invention, therefore, is to be determined solely by the
following claims.
* * * * *